Apparatus of this type are well known and have numerous applications, notably in the field of portable telephones for which the circuit to be charged is formed by a battery located in the housing that forms the handset. This battery is to be recharged by an energy source formed by a charging circuit connected to the power grid.
A problem which is posed with apparatus of this type is that the charging voltage of the battery should be well adapted to the battery. Notably for lithium-ion batteries this voltage is to be 4.1 volts plus or minus 1%. If the charging voltage is below this value, the battery is never charged well and if the voltage is too high, one runs the risk of a deterioration of the battery or else an explosion.